Special Signal modules
5-11
Programmable Logic Controllers S7-300 Module Data
A5E00105505-03
5.4.5 Gray/Dual Converter
In the Gray setting, the encoder values provided by the absolute value encoder in
gray code is converted into Dual code. In the Dual setting, encoder values
provided by the absolute value encoder remain unchanged.
Note
If you have selected the Gray setting, the SM 338 always converts the entire
encoder value (13, 21, 25 bits). As a result, preceding special bits affect the
encoder values and following bits could be falsified under certain circumstances.
5.4.6 Transferred Encoder Value and Normalization
The transferred encoder value contains the encoder position of the absolute value
encoder. Depending on the encoder used, additional bits which are located before
and after the encoder position are also transferred in addition to the encoder
position.
So that the SM 338 can detect the encoder position, make the following settings:
• Normalization, places (0..12), or
• Normalization, units / revolution
Normalization, places
The normalization determines the position of the encoder values in the checkback
interface.
• If “Places” = 1, 2....12, this indicates that the following non relevant bits in the
encoder values are removed and the encoder value is right justified in the
address range (see following example).
• If “Places” = 0, this indicates that the following bits are retained and available
for evaluation.
This can be useful if you use an absolute value encoder which transfers
information in the following bits (see manufacturer information) and you want to
evaluate these (see also chapter 5.4.5).
Parameter units / revolution
A maximum of 13 bits are available for the units/revolution. According to the
“Places” data, the resulting number of units/revolution is automatically displayed.
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